android - 按回不返回到上一个 fragment

Question

我在将 fragment 事务添加到后台堆栈时遇到问题。我有一个主要 Activity ，其中我用菜单 fragment 填充我的布局:

public class MainActivity extends ActionBarActivity{

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getFragmentManager().beginTransaction().add(R.id.frag_container, new MainMenuFragment()).commit();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

然后，在 MainMenuFragment 中，用户选择一些选项，结果用其他 fragment 替换菜单 fragment :

public class MainMenuFragment extends Fragment implements OnItemClickListener{
    GridView grid;
    FragmentManager manager;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View root = inflater.inflate(R.layout.main_menu_fragment, container, false);

    manager = getActivity().getFragmentManager();
    grid = (GridView) root.findViewById(R.id.gridView1);

    grid.setAdapter(new MenuTileAdapter(getActivity()));
    grid.setOnItemClickListener(this);

    return root;
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    FragmentTransaction trans = manager.beginTransaction();
    if (position == 0){
        trans.replace(R.id.frag_container, new BasicSettingsFragment());
        trans.addToBackStack(null);
        trans.commit();
    }
}

就我的理解，这应该使得当用户按下他们设备上的后退按钮时，他们将被带回菜单 fragment ，但是这会退出应用程序。我做错了什么？

Answer 1

在您的 Activity 中覆盖:

@Override
public void onBackPressed() {
    if (getFragmentManager().getBackStackEntryCount() > 0) {
        getFragmentManager().popBackStack();
    } else {
        super.onBackPressed();
    }
}

并且您可能需要在每个提交的 fragment 事务中使用:

FragmentTransaction.addToBackStack(null);